1. Technical Field
The disclosure relates to a processing device for processing a pixel signal, an imaging device, and an endoscope system.
2. Related Art
Conventionally, in the medical field, an endoscope system is used to observe the inside of a subject. In general, the endoscope system captures an in-vivo image by inserting a flexible insertion unit having an elongated shape into the subject such as a patient, intermittently emitting illumination light from the distal end of the insertion unit, and receiving reflected light of the illumination light by using an imaging unit at a distal end portion of the insertion unit. The in-vivo image captured in this way is displayed on a display of the endoscope system.
When imaging is performed under intermittent illumination, a variation in brightness occurs between images depending on an exposure timing of an image sensor, so that the images may flick when the images are displayed on the display. In particular, when employing a CMOS (Complementary Metal Oxide Semiconductor) image sensor and applying a rolling shutter method that changes timing of exposure and reading for each horizontal line, an exposure timing varies for each horizontal line in one imaging period, so that luminance unevenness easily occurs.
In order to address such a situation, conventionally, a technique is proposed that generates a display image by removing areas having luminance greater than or equal to a predetermined threshold value from a frame image (for example, see JP 2010-135921 A). In addition to the technique described in Patent Literature 1 that removes part of an image, a technique is also proposed that can secure a certain level of luminance in the entire area of an image by causing a light source to emit illumination light in a period common to all pixels in an exposure period of each pixel of an image sensor (for example, see JP 2009-136447 A).